Isomerization of olefins



Patented Sept. 7, 1943 ISOMERIZATION OF OLEFINS Charles L. Thomas, Chicago, 111., assignor to Universal Oil Products Company, Chicago, 111., a

corporation of Delaware No Drawing. Application January 20, 1939, Serial No. 251,947

8 Claims.

The invention relates to the isomerization of hydrocarbons and pertains more specifically to the catalytic isomerization of olefin hydrocarbons. By this process relatively straight chain olefinic hydrocarbons are converted into branched chain oleflnic hydrocarbons or slightly branched chain olefins are converted into more branched chain olefins.

With the rapid rate of development of hydrocarbon technology, isomerization of hydrocarbons assumes important aspects. Frequently the normal olefins are more available than the isoolefins and for some uses it becomes highly desirable to convert the normal into the iso-olefins. The present invention involves the conversion of olefinic hydrocarbons in the presence of specific types of catalytic materials which function to selectively isomerize normal 'olefinic hydrocarbons with the formation of large yields of iso-olefins under suitable conditions of operation. The preferred catalysts are prepared synthetically by definite steps of procedure which are specific in the production of catalysts of high activity for prolonged use. Many catalysts used in hydrocarbon reactions generally such as reduced metal catalysts, particularly iron and nickel, accelerate reactions leading to the formation of gas and these catalysts also have the disadvantage of being readily poisoned and quickly coated with carbonaceous material. Many metal oxide catalysts which are available accelerate principally dehydrogenation reactions. The preferred catalysts used in the present invention, however, are characterized by their selectivity in accelerating the desired isomerization reaction, by their ease and simplicity of manufacture, their exact reproducibility and their refractory nature which enables them to retain their catalytic properties over extended periods of time under high temperature conditions of use and regeneration.

In one specific embodiment the present invention comprises subjecting relatively straight chain normal olefinic hydrocarbons at elevated temperatures and at atmospheric to moderately super-atmospheric pressures to contact with catalytic materials comprising synthetically prepared calcined composites of hydrated silica and hydrated alumina producing high yields of iso-olefinic hydrocarbons. In a further embodiment the catalytic materials comprise synthetically prepared composite masses of hydrated silica and hydrated zirconia.

In the description of the catalysts of the present invention they are referred to as silica-alumina or silica-zirconia catalysts since compounds represented by the symbols SiO2, A120: and Zr02 are involved. Inasmuch as the chemistry of the true solid states is very incompletely developed. it has not been determined how these materials are arranged within the catalyst. These catalysts may be prepared by a number of alternative methods which have certain necessary features in common as will be subsequently described. Generally speaking, however, the catalysts may be considered to comprise a combination of silicon and aluminum or silicon and zirconium with oxygen, possibly an intimate molecular admixture of silica-alumina and silica-zirconia all of the components of which indicate more or less low activity individually but in the aggregate display high activity. The activity is not anadditive function, it being relatively constant for a wide range of proportions of the components whether in molecular or fractions of molecular proportions. No one component can be determined as the one component for which the remaining components may be considered as the promoters according to conventional terminolo y, nor can any component be determined as the support and the others the catalyst proper. In the description of the preparation of the preferred catalysts given below precipitated hydrated zirconia may be composited with hydrated silica gel and salts of zirconium may be used as when preparing silica-alumina catalysts although the catalysts produced therefrom do not necessarily give equivalent results. It has been found in some cases that the silica-zirconia composites have greater stability over prolonged periods of use than have some silica-alumina catalysts.

According to one general method of preparation used before drying treatment, the preferred catalysts may be prepared by precipitating silica from a solution as a gel and subsequently admixing or depositing hydrated alumina upon the hydrated silica. One of the more convenient methods of preparing the silica gel is to acidify an aqueous solution of sodium silicate by the addition of an acid such as hydrochloric acid, for example. The excess acid and the concentration of the solution in which the precipitation is brought about determine in some measure the suitability of the silica, hydrogel for subsequent compositing with hydrated alumina. In general, suitable hydrated silica may be produced by the use of dilute solutions of sodium silicate and the addition of a moderate excess of acid whereby the desired active silica gel is obtained and conditions of filtering and washing are at an optimum.

After precipitating the hydrated silica it is treated and washed to substantially remove alkali metal ions. It is not known whether the alkali metal ions such as sodium ions are present in the primary gel in chemical combination or in an adsorbed state but it has been definitely determined that their removal is necessary if catalysts suitable for prolonged use in accelerating isomerization reactions are to be obtained. It is possible that the presence of the alkali metal impurities causes' a sintering or fluxing of the' surfaces of the catalyst at elevated temperatures so that the porosity is much reduced with corresponding reduction in eifectiv surface. Alkali metal ions may be removed by treating with solutions of acidicmaterials, ammonium salts generally, or salts of aluminum. When treating with acids, as for example, with hydrochloric acid, the acid extracts the alkali metal impurities in the silica, gel. The salts formed and acid are then substantially removed by water washing treatment. Where ammonium salts or salts of aluminum are used, the ammonium or aluminum apparently displaces the alkali metal impurities present in the composite and the alkali metal salts formed together with the major portion of the aluminum salts are removed in the water washing treatment. Some of the aluminum introduced into the silica hydrogel in the purifying treatment becomes a permanent part of the composite, whereas, in the treatment with ammonium salts which are present in relatively small amounts, they will be driven oil in subsequent treatment at elevated temperatures.

In one of the preferred methods of compositing the hydrated materials, the purified precipitated hydrated silica gel maybe suspended in a solution ofaluminum salts in the desired proportions and hydrated alumina deposited upon the suspended hydrated silica by th addition of volatile basic precipitants such as ammonium hydroxide, for example, or ammonium carbonate. ammonium hydrosulfide, ammonium sulfide or other volatile basic precipitants such as organic bases may be employed. According to this method, the purified silica gel may be suspended in a solution of aluminum chloride, for example, and the hydrated alumina precipitated by the addition of ammonium hydroxide.

Alternatively the purified hydrated silica gel may be mixed while in the wet condition with separately prepared hydrated alumina precipitated as for example by the addition of volat le basic precipitants to solutions of aluminum salts. The hydrated alumina thus prepared is substantially free from alkali metal ions and can be admixed with the purified silica gel. However, if alkali metal ions are incorporated as when the .hydrated alumina is prepared from sodium alu minate, for example, regulated treatment and water washing would be required by methods selected from those described in connection with the purification of the hydrated silica gel to remove alkali metal ions. Care should be observed in the selection and concentration of reagents used so as not to dissolve unduly large amounts of alumina. As further alternatives the purified silica gel may be added to a solution of an aluminum salt and the alumina deposited'by hydrolysis with or without the use of heat, or the purified silica gel may be mixed with suitable amounts of salts of aluminum as, for example, in forming a paste and heating whereby alumina is deposited upon the silica gel as a result of the decomposition of the aluminum salt.

In the methods above described, a silica hydrogel free from alkali metal ions was admixed with or had deposited thereon relatively pure hydrated alumina prior to drying treatment. methods described below, the hydrated silica and hydrated alumina are concurrently precipitated or admixed and treated to remove alkali metal ions from the composited material prior to drying treatment either in presence of th original reactants or subsequent to water washing. Thus,

solutions of silicon compounds more usually alkali metal ilicates and soluble aluminum salts may be mixed under regulated conditions of acidity or basicity to jointly precipitate hydrated silica and hydrated alumina in varying proportions. For example, solutions of sodium silicate and aluminum chloride may b mixed and alkaline or acid reagents added according to the proportions used so that a pH of 3-10 is obtained. In cases where a sol is formed the precipitation may 'be brought about if the sol is acid by addition of a volatile base as, for example, ammonium hydroxide and alkali metal salts removed by water washing, or the composite may be treated as indicated above in connection with the purification of the hydrated silica to remove alkali metal ions. Various methods are possible for the preparation of the hydrated silica and hydrated alumina separately or in combination and the purifying treatment is necessary where alkali metal ions are present in substantial amounts.

The character and efliciency of the ultimately prepared silica-alumina catalyst will vary more or less with precipitation and or mixing, purification treatment, ratio of components, calcining, etc., several specific examples being given. The ratio of the components may be varied within wide limits, the limiting factor with respect to activity [being more in evidence with small proportions than with larger proportions of the added component. In general, it appears that two to six atoms of one component per hundred atoms of the remaining component may be considered an approximation of the minimum proportions;

After the alumina has been mixed or composited with the purified hydrated silica gel and water washed if desired, as described for one general method of preparation, or after the hydrated silica and hydrated alumina have been composited and treated to remove alkali metal ions, as described for another general method or preparation, the catalytic material may be recovered as a filter cake and dried at a temperature of the order of 240-300 F. more or less, after which it may be formed into particles of a suitable size ranging from powder to various formed sizes obtained by pressing and sizing or otherwise formed before or after drying into desired shapes by extrusion or compression methods for example.

By calcining at temperatures of the order of approximately 850-Q F., or higher} maximum activity of th catalyst is obtained and a further dehydration occurs so that, for example, after a considerable period of heating at 900 F., the water content as determined by analysis is of the order of 2-3 percent.

Catalysts prepared by the various types of procedures outlined evidently possess a large total contact surface corresponding to a desirable porosity, the pores of the catalyst particles being of such size and shape that they do not become clogged with carbonaceous deposits after a long period of service, and therefore, diflicult to reactivate by oxidation. This structure is also retained after many alternate periods of use and reactivation as evidenced by the fact that the catalysts may be repeatedly reactivated by passing air or other oxidizing gas over the spent particles to burn off deposits of carbonaceous material at temperatures above 800 F., temperatures as high as 1400-1600 F. being reached without apparently affecting the catalytic activity.

In accordance with the present invention the catalysts may be conveniently utilized in isomerizing hydrocarbons when employed as filling material in tubes or chambers in the form of small pellets or granules. The average particle size may be within the approximate range of 1-10 mesh, which may apply either to pellets of.,uniform size and short cylindrical shapes or to particles of irregular size and shape produced by the grinding, consolidating and sizing of the partially dehydrated materials. While the simple method of preheating the hydrocarbon vapors to a temperature suitable for their isomerization in contact with the catalysts and then passing the vapors over a stationary mass of catalyst particles may be employed in some cases it may be preferable to pass the preheated vapors through or around a plurality of relatively small diameter tubes in multiple and parallel connection having catalyst disposed in or around said tubes since this arrangement of apparatus is better adapted to permit heating and cooling of the catalyst masses to compensate for the heat absorbed in the endothermic isomerizing reactions and t 11 pate heat in the regeneration. After the passage of the hydrocarbon vapors over the catalysts, the products are separated by fractionation.

The temperatures employed in contact with the catalysts will vary according to the olefinic hydrocarbons charged to the process, the temperatures used, however, being within the range of 400 to 1050 F. When processing any particular fraction of these hydrocarbons shorter contact times are used for th higher temperature. Substantially atmospheric pressure or moderately superatmospheric pressure up to 90 pounds per square inch or more may be used such pressures being somewhat governed by flow conditions through the vaporizing and conversion zones and the subsequent separating, fractionating and collecting equipment.

The following specific examples are given to illustrate the process of the invention, the methods of catalyst preparation also being given. The process should not be considered as limited to these examples or to the particular catalyst preparations these being given as illustrative of the novelty and utility or the invention.

A catalyst was prepared as follows, having hydrated silica and hydrated alumina in the following proportions, 100SiO2t5A12O3. A solution of commercial sodium silicate was prepared corresponding to 480 grams of SiOz in '7 liters of Water. To this was added slowly while agitating 1350 cc. of dilute hydrochloric acid'solution (containing 562 cc. of concentrated acid). A silica hydrogel was formed which was directed to a filter and subsequently carefully water washed including a wash with dilute ammonium chloride solution, the washed silica gel being recovered as a filter cake. A portion of this cake corresponding to 84grams of SlOz was slurried in a solution of 34 grams of aluminum chloride hexahydrate in 1500 cc. of water. Ammonium hydroxide was then added until the liquid was basic to red litmus paper whereby hydrated alumina was precipitated in the presence of the suspended hydrated silica. The suspension was then directed to a filter and filter cake obtained which after drying at'approximately 300 F. was powdered and consolidated. Granules of 6-10 mesh were prepared and calcined at approximately 900 F. prior to contacting with the hydrocarbon vapor.

When catalyst prepared as above is disposed in a chamber and 98% pure pentene-1, for example, is vaporized and directed through. the catalyst at approximately 775 F. and substantially atmospheric pressure using a liquid space velocity per hour of approximately 4, the product comprises 10% gas, 70% of a C5 fraction and 15% of higher boiling material. The C5 fraction comprises 78% of isopentenes corresponding to 55% yield based on the pentene charged to the process.

As a further example when vaporizing a mixture of l and 2 normal octenes and directing through the silica-alumina catalyst at approximately 710 F. and substantially atmospheric pressure using a liquid space velocity per hour of approximately 4, a yield of 50.4% by weight of charge of iso-octenes was produced in a 1 single pass, approximately 12% of the products being unconverted octene and approximately 14% being normally gaseous hydrocarbons.

As an example of a similar'operation on normal octenes using a silica-zirconia catalyst of the following proportions, 1O0SiO230ZIOz, prepared similarly as the silica alumina catalyst above described, a yield of 57.4% by weight of the charge of iso-octenes was produced, 17.8% of unconverted normal octene being present in the product and 13.7% of normal gaseous hydrocarbons.

Considerably lower and higher space velocities may be used in the process of the present invention which is not considered as limited in this respect, and various olefinic hydrocarbons or mixtures thereof with or without the presence of other hydrocarbons may be processed.

I claim as my invention:

1 A process for isomerizing aliphatic olefins of at least 4 carbon atoms to the molecule, which comprises contacting the olefins at isomerizing temperature with an isomerizing catalyst substantially free of alkali metal ions comprising a calcined mixture of precipitated hydrated silica and a hydrated oxide selected from the group consisting of precipitated alumina and precipitated zirconia, and correlating the reaction temperature and time of contact of the olefins with the catalyst to eilect olefin isomerization as the principal reaction in the process with minimum olefin polymerization.

2. A process for improving the motor fuel characteristics of aliphatic olefins boiling in the gasoline range which comprises contacting the olefins at isomerizing temperature with an isomerizing catalyst substantially free of alkali metal ions and comprising a calcined mixture of precipitated hydrated silica and a hydrated oxide selected from the group consisting of precipitated alumina and precipitated zirconia, and correlating the reaction temperature and time of contact of the olefins with the catalyst to efiect olefin isomerization as the principal reaction in the process with minimum olefin polymerization.

3. The process as defined in claim 1 further characterized in that said isomerizing temperature is in the approximate range of 4001050 F.

4. The process as defined in claim 2 further characterized in that said isomerizing temperature is in the approximate range of 400-1050" F.-

5. A process for isomerizing aliphatic oleflns 01 at least 4 carbon atoms to the molecule, which comprises contacting the olefins at isomerizing temperature with an isomerizing catalyst substantially free of alkali metal ions and comprising a calcined mixture of precipitated hydrated silica and precipitated hydrated alumina, and correlating the reaction temperature and time of contact of the olefins with the catalyst to effect olefin isomerization as the principal reaction in the process with minimum olefin polymerization.

6. A process for improving the motor fuel characteristics of normal olefins boiling in the gasoline range which comprises contacting the olefins at isomerizing temperature with an isomerizing catalyst substantially free of alkali metal ions and comprising a calcined mixture of precipitated hydrated silica and precipitated hydrated alumina, and correlating the reaction temperature and time of contact of the olefins with the catalyst to effect olefin isomerization as the principal reaction in the process with minimum olefin polymerization.

7. A process for isomerizing aliphatic olefins of at least 4 carbon atoms to the molecule, which comprises contacting the oleflns at isomerizing temperature with an isomerizing catalyst substantially free of alkali metal ions and comprising a calcined mixture or precipitated hydrated silica and precipitated hydrated zirconia, and

correlating the reaction temperature and time I of contact of the oleflns with the catalyst to efprecipitated hydrated sflica and precipitated.

hydrated zirconia, and correlating the reaction temperature and time of contact of the oleflns with the catalyst to effect olefin isomerization as the principal reaction in the process with minimum olefin polymerization.

. CHARLES L. THOMAS. 

